Limit switch for electric hoists



May 12, 1925.

I 1,537,774 S. E. KALBACH LIMIT SWITCH FOR ELECTRIC HOISTS Filed o -11. 1924 2 Sheeds-Sheet 1 May 12, 1925.

s. KALBACH LIMIT SWITCH FOR ELECTRIC HOISTS Fiied Nov. 11, 1924 2 Shee'tsrShe-et 2 Patented May 12, 1925,

UNlTED STATES-PATENT OFFICE.

SAMUEL E, KALBACH, OF READING, PENNSYLVANIA, ASSIGNOR TO ROEPER CRANE AND I-IOIST WORKS, OF READING, PENNSYLV N ORPORATION OF PENN- SYLVANIA.

LIMIT SWITCH FOR, ELECTRIC HOISTS.

Application filed November 11, 1924. Serial No. 749,212.

r pact unit.

The invention consists of a limit switch whereby an automatically predetermined stopping of a hoist, at both the top and bottom limit of its travel, is assured, and in which an overrunning of the machine is positively prevented.

As an assembled device, the entire appa ratus consists of a timing gear, a threaded shaft having adjustable top and bottom stops, a self centering arrangement for the shaft and two sets of contacts and the whole encased in a suitable enclosure.

The invention is more fully described in the following specification and clearly illustrated in the accompanying drawings, in which Figure 1 is a side elevational view of the device.

Figure 2 is a longitudinal sectional view through the line 22 of Figure 1.

Figure 3 is an end View taken in the di rection of the arrow 3, Figure 1.

Figure 4 is a sectional view on line 44 of Figure 2.

The numeral 1 designates the casing in which the entire device is enclosed. 2 designates the timing gear and 3 the stop shaft. This shaft is threaded and the gear is provided with a steel hub bushing and it rotates on the threaded shaft.

The threaded shaft is provided with adj ustable limit stops 4 and this shaft is prevented from turning within a certain zone, by a centering device, which consists of a double acting compression spring 6, a collar 7 around which the spring is wound and the collar is provided with a key 8 having its bearing upon the shaft.

The numeral 10 designates the electrical contacts, which may be either single or double pole contacts, depending on whether direct or alternating current is used. These contacts comprise fingers 11, held in normal position by springs 13, with the circuits closed, where they remain so long as the shaft stops do not contact with either of them.

The rotation of the gear 2 will cause the threaded shaft 3 to move longitudinally, but it will be held against rotation by the centering device, until it has reached the point where one of the adjustable stops 4 is brought into contact with one of the spring backed fingers 11 of the electrical contacts. The stops and the fingers are each formed with registering lugs 15, so that, when one of the stops slides into engagement with one of the fingers, that is, when the thread ed shaft has travelled its predetermined dis tance, in either direction, this engagement of the stop with the finger will prevent any further longitudinal or sliding movement of the shaft, but the shaft will be caused to rotate because of the gear overcoming the resistance of the centering device, and this will cause the finger to be moved and the power cut OH in one direction. The shaft 3, it will be noted, will rotate only when one of the stops engages one of the fingers, that is, when the shaft has reached its predetermined travel, and this cutting off of the power in one direction will not prevent the motor from operating in the opposite direction.

The distance of travel of the shaft 3 is of course predetermined by the adjustable stops 4.

The two electrical contacts are held normally closed, completing the power circuit of a reversible motor (not shown) for either clockwise or counterclockwise rotation and will remain so within the safety zone fixed by the stops 4.

It is evident that, either of the contacts having been lifted, will, upon reversal of the motor, and through the action of the centering device, reset itself.

What I claim is 1. In a limit switch for electric hoists, the combination of a timing gear, a threaded shaft, means for holding the shaft against rotation while it moves longitudinally, ad-. justable stops on the shaft, electric contacts having sl jring-backed fingers thereon, regis tering lugs on the stops and on the fingers whereby contact of the stops with the fingers will stop the lon'gi tu'dinal inoveinei'it of the shaft and cause it to rotate and open one of the contacts.

2. In a device of the character described, a timing gear, a threaded stop shaft on which the gear turns, an adjustable stop on the shaft, a lug on said stop, means for holding the shaft against rotation While it is moved laterally by the rotation of the gear, an electric contact, afinger thereon, a lug on the finger to register Wlfll tllB lug on the stop, whereby when the shaft has been "moved a predetermined distance the contact of the said lugs Will stop the lateral movement of the shaft and cause a rotation thereof to efiect the opening of the electric contact. H

In testimony whereof I afiix my signature.

SAMUEL E. KAIJBAGH. 

